With increasing demand for improved thermal performance of casement windows, and the desire for larger window openings, there is an increasing demand for casement window hardware that can handle increasingly larger and heavier window sashes. As sash size increases the load borne by casement window hardware increases dramatically. On prior art concealed casement hinges, the amount of friction between the sliding shoe and the track is one of the conditions that limit the maximum weight that a window hardware system can handle. As the window sash weight increases, the sliding friction in the hinge increases and greater loads are placed on the sash operator mechanism to overcome that friction. This can lead to premature failure of the operator mechanism. Increased sash weight also increases the amount of wear on the lower sliding hinge shoe.
The potential for damage to the hinge during shipping and handling also increases as the sash weight is increased. Handling of window units during shipping is not always careful. When a heavy window unit is dropped, even from a small distance, high impact loads are transmitted though the hinges unless the sash is otherwise supported within the frame, such as by multiple shipping blocks wedged between the sash and frame.
Shipping blocks fill the space between the frame and the sash and transmit loads encountered during shipping from the frame to the sash instead of to hinges or other hardware. Shipping blocks thereby prevent damage to the hardware.
One prior attempt at a high-load capacity hinge included two rollers built into the shoe. A disadvantage of this hinge design, however, is that it requires additional shims, shipping blocks or other shipping preparations to prevent high impact loads incurred during shipping and handling from being transmitted directly onto the shoe rollers and axles. Otherwise, damage to the rollers and shoe can occur. This design also has two rollers to support the sash weight, adding to the complexity and increasing the part count of the hinge.
Another problem encountered with prior hinges when used with the bending loads imposed by heavy sash components in the opening and closing process is that the sliding shoe may be broken or may become detached from the track due to breakage or deformation of the track.
Accordingly, there is still a need in the industry for a high-load capacity casement window hinge that addresses the drawbacks of prior devices.